Conventionally, there is a frame transmitting apparatus that transmits a packet frame (see, e.g., Japanese Laid-open Patent Publication No. 2006-197045).
A brief description is provided below with reference to FIG. 6 regarding processing performed by the conventional frame transmitting apparatus for transmitting a packet frame.
As depicted in FIG. 6, a frame transmitting apparatus 200 is connected in a communication-capable state with a prior apparatus 100 and a subsequent apparatus 300 of a same configuration via a network.
A frame monitoring unit 201, upon detection of input of a received frame transmitted by the prior apparatus 100, generates a timing signal to indicate timing of processing of the received frame and outputs the timing signal to subsequent processing function units.
Next, an FCS monitoring unit 202, after checking the received frame, using FCS (Frame Check Sequence) data for error detection appended to the received frame, deletes the FCS data from the received frame and outputs the received frame to a header termination unit 203.
The header termination unit 203 outputs a header within the received frame that stores an address, a tag, length, etc., to a header control unit 204 and cuts out user data within the received frame and outputs it to a scrambling unit 205.
The scrambling unit 205 performs scrambling processing on the user data and outputs the scrambled user data to a parity generating unit 206. The parity generating unit 206 appends a parity to the scrambled user data and outputs the resulting data to a memory 207.
The memory 207, under control of the header control unit 204 to be described later, writes the data received from the parity generating unit 206 and reads out the data and outputs the read-out data to a parity monitoring unit 208 to be described later.
The header control unit 204 manages the address of the data to be stored in the memory 207 and causes the memory 207 to output the stored data to the parity monitoring unit 208. The header control unit 204 also rewrites the header received from the header termination unit 203 and outputs the resulting data to a header inserting unit 210.
The parity monitoring unit 208 performs a parity check of the data received from the memory 207 and outputs the resulting data to a descrambling unit 209. The descrambling unit 209 performs descrambling processing on the data received from the parity monitoring unit 208 and outputs the resulting data to the header inserting unit 210.
The header inserting unit 210 appends the header received from the header control unit 204 to the data received from the descrambling unit 209 and outputs the data to an FCS calculating unit 211.
The FCS calculating unit 211 performs FCS calculation and appends FCS data to the data received from the header inserting unit 210 and transmits the data to the subsequent apparatus 300 via the network.
However, the above conventional frame transmitting processing has had a problem that there is a case of not detecting an error occurring in the process of the transmitting processing of the received frame.
Namely, the conventional processing has had a problem that when, at the time of writing the user data to the memory 207, the parity appended to the user data makes 2 bit errors, occurrence of the error to the user data may not be detected.
The conventional processing has had a problem that, likewise, the error caused to the user data by malfunction of the scrambling unit 205 may not be detected.
While it is possible to process by writing to the memory 207 the data with the error-detection FCS left appended thereto, such processing causes a large amount of data to be written, and therefore, has a problem that a memory size must be enlarged.